• 한국항행학회논문지
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• 제6권3호
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• pp.203-210
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• 2002

본 논문에서는 IEEE 802.11a의 규격에 따라 OFDM 우선 LAN 모뎀과 프레임 포맷을 구성하여 시뮬레이션에 의해 BER 성능을 분석하고 수정된 채널 예측 알고리즘을 적용하여 채널예측성능이 개선됨을 보인다. 채널 예측에 이용되는 실내 무선채널로서는 AWGN과 TDL 모델을 적용한 지연확산채널을 고려한다. 우선 AWGN 환경에서 규격에 제시된 전송속도 및 부호율에 따른 OFDM 무선 LAN 시스템의 성능을 분석한다. 다음으로 실내 우선 채널 환경에서 채널추정이 불완전한 경우에 대해, 기존의 채널추정방식으로서 프리앰블 내의 2개의 Long 훈련심볼을 이용하여 채널을 추정하는 경우에 대한 성능을 분석하고, 수정된 채널추정기법으로는 IEEE 802.11a의 프리앰블 구조를 변경하지 않으면서 Long 훈련심볼뿐만 아니라 전체 10개의 Short 훈련심볼 중 8개의 훈련 심볼들을 채널추정에 부가적으로 사용하는 방식을 채용한 경우의 성능을 분석하여 기존의 방식과 비교한다. 시뮬레이션 결과의 분석으로부터 수정된 채널추정방식을 적용하는 경우, 규격에 정의된 프리앰블 구조의 변경 없이도 잡음을 억제하는 효과를 향상시킴으로써 채널추정오차가 감소되어 채널추정성능이 개선됨을 확인하였다.

• 한국유통학회지:유통연구
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• 제2권1호
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• pp.59-85
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• 1997

The automobile industry in Korea has grown to the fifth in the world in terms of production capacity. In spite of the production growth, the marketing aspects such as distribution and customer service in the auto industry are still behind the world-class. Thus, the major purposes of this paper are as follows. The first is to analyze competitive structure of the industry and to compare distribution strategies of the major auto firms(Hyundai, Daewoo, and Kia). The second is to theoretically explain the transition from the vertical marketing system to the dealer system using transaction cost analysis. The third is to compare auto distribution channels in Korea with those in the U.S. and Japan. Finally, an optimal channel stucture in the auto industry is suggested after reviewing five alternative channel structures such as corporate-owned VMS, sales-specializing firm, multiplex system(VMS+limited dealer system), dual sales channel, and advanced dealer system. In the short-run, sales-specilizing firm was suggested as an optimal channel system to enhance customer satisfaction by integrating sales and customer service. In the long-run, advanced dealer system through regional differentiation was desirable for an optimal channel structure by organically integrating new car sales, used car sales, and after service to provide total marketing service to customers.

• ETRI Journal
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• 제29권4호
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• pp.430-436
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• 2007

An OFDM/offset QAM (OQAM)-IOTA system uses the isotropic orthogonal transform algorithm (IOTA) function, which has good localization properties in the time and frequency domains. This is employed instead of the guard interval used in a conventional OFDM/QAM system in order to be robust for multi-path channels. However, the conventional channel estimation scheme is not valid for an OFDM/OQAM-IOTA system due to the intrinsic inter-symbol interference of the IOTA function. In this paper, a condition is derived to reduce the intrinsic interference of the IOTA function. This condition is obtained with the proposed pilot structure used for perfect channel estimation. We also derive the preamble structure appropriate for practical channel estimation of the OFDM/OQAM-IOTA system. Simulation results show that the OFDM/OQAM-IOTA system with the proposed preamble structure performs better than the conventional OFDM system, and it has the additional advantage of an increased data transmission rate which corresponds to the guard interval retrieval.

• 융합신호처리학회 학술대회논문집
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• 한국신호처리시스템학회 2003년도 하계학술대회 논문집
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• pp.110-113
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• 2003

In this paper, the multi-channel high speed data acquisition system is implemented. This high speed signal processing system for 3-D image display is applicable to the manipulation of a medical image processing, multimedia data and various fields of digital image processing. In order to convert the analog signal into digital one, A/D conversion circuit is designed. PCI interface method is designed and implemented, which is capable of transmission a large amount of data to computer. In order to, especially, channel extendibility of images acquisition, bus communication method is selected. By using this bus method, we can interface each module effectively. In this paper, 32-channel A/D conversion and PCI interface system for 3-dimensional and real-time display of the retina image is developed. The 32-channel image acquisition system and high speed data transmission system developed in this paper is applicable to not only medical image processing as 3-D representation of retina image but also various fields of industrial image processing in which the multi-point realtime image acquisition system is needed.

• Journal of electromagnetic engineering and science
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• 제7권2호
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• pp.83-90
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• 2007

In this paper, the formulation of the protection ratio based upon a composite fade margin and availability is newly presented for the detailed planning of frequency coordination in the microwave relay system network, and computed results for co-channel and adjacent channel protection ratios are illustrated over an actual system with 6.2 GHz. It is shown that the protection ratio to assure a quality of service can be expressed in terms of the composite fade margin, noise-to-interference ratio, net filter discrimination, and system parameters. In addition, the net filter discrimination, depending upon the transmitter spectrum mask and the overall receiver filter characteristic, has been examined to investigate the effect of the adjacent channel protection ratio caused by the adjacent channel interference. Regarding simulated results for 6.2 GHz, 60 km, 64-QAM, and N/I=6 dB at the bit error rate of $10^{-6}$, composite fade margin and co-channel protection ratio yield 25.14 and 50.3 dB, respectively. Also, the net filter discrimination of 26.5 dB and the adjacent channel protection ratio of 23.8 dB are obtained at the first adjacent channel of 30 MHz. The proposed method provides some merits in view of a comprehensive and practical application with more detailed and various system parameters needed to access the criteria for making the proper frequency coordination.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 하계종합학술대회 논문집(1)
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• pp.97-100
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• 2001

The performance of mobile radio communication system is dependent on various factors such as channel environment. Especially, the number of multipath components of mobile radio channel and multipath delay property in CDMA system for different bandwidths are changed. Therefore, using multipath components, Rake receiver provides improvement of performance of W-CDMA system is evaluated by computer simulation over the types of ITU-R wideband channel model and spreading rate. The result shows that the performance of CDMA adapting RAKE receiver is Improved by the increase of multipath components in equal level of the received power.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 통신소사이어티 추계학술대회논문집
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• pp.277-280
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• 2003

In this paper, we analyze the performance of transmitter and receiver of W-CDMA system using the channel coding and space time code in downlink over ITU-R realistic channel model. We can improve the reliability of communications and increase the data rate by channel coding, and we can get a diversity gain by using the space time code over fading channels. We also apply the RAKE receiver to improve tile performance in multi-Path fading channel environment.

• 한국전자파학회논문지
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• 제27권10호
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• pp.900-908
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• 2016

본 논문에서는 일반적인 3채널 구조의 모노펄스수신기와 대비해서 비용, 크기, 무게 및 소모전력 측면에서 유리한 단일채널 구조의 모노펄스수신기를 적용한 추적시스템에 관한 연구를 진행하였다. 안테나, 모노펄스수신기, 구동체, RF 신호처리기 및 전원분배기를 제작 및 통합하여 단일채널 모노펄스시스템을 구현한 후, 지향오차각 산출정확도와 포인팅 손실을 측정하여 기본 추적성능을 확인하였다. 그리고 야외환경에서 실제 이동하는 목표물에 대한 추적성능을 검증하였다. 시험결과 분석을 통해 단일채널 모노펄스시스템이 일반적인 3 채널 모노펄스시스템과 동등 이상의 추적성능을 가지면서 시스템의 구현측면에서 이점이 있음을 확인하였다. 또한, 이 연구로 향후 모노펄스 추적시스템 개발 시 제작비용 및 제품 소형화에 유리한 단일채널 모노펄스수신기 적용이 가능함을 확인하였다.

• 전자공학회논문지
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• 제53권3호
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• pp.11-20
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• 2016

본 논문에서는 LTE-A (Long Term Evolution-Advanced) 하향링크 시스템을 위한 채널 추정 기법을 제안한다. 제안 기법은 빠른 속도로 움직이는 사용자의 채널 추정이 가능하도록 FFT (Fast Fourier Transform) 보간 기법을 사용한다. FFT 보간 기법은 LS (Least Square) 또는 MMSE (Minimum Mean Square Error) 채널 추정으로부터 얻은 채널 주파수 응답을 IFFT (Inverse FFT)를 거쳐 시간 영역 채널 임펄스 응답으로 변환한다. 시간 영역의 채널 응답을 윈도잉을 한 후, FFT를 하여 채널 주파수 응답을 구할 수 있다. 시스템 레벨 시뮬레이션은 3GPP LTE-A 하향링크 시스템의 20MHz 대역을 기반으로 이루어졌으며, 모의실험 결과 제안한 채널 추정 기법을 통해 기존 시스템보다 SINR (Signal-to-Noise-plus-Interference Ratio), 전송률 및 스펙트럼 효율 측면에서 성능 향상을 가져다주는 것을 확인하였다.

• 방사선산업학회지
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• 제6권3호
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• pp.231-237
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• 2012

This paper introduces a gamma-ray measurement system for a transportable tomography which is applicable for an industrial process diagnosis. The gamma-ray measurement system consists of pulse mode operating 72 channel CsI detectors, main AMP-pulse shaper, single channel analyzer, counter and control PC. The CsI crystal is coupled with a PIN diode which is connected to an amplifier and pulse shaper. For a compact design, the amplifier and pulse shaping circuit are included in a single package. 36 sets of CsI detectors are connected to a multi-channel counter through single channel analyzers. A computer controls and collects data from two multi-channel counters. This configuration results in 72 channel counting system in total. The CT rotator and radiation measurement system are controlled by a PC with LabVIEW program. Tomographic data were measured for a phantom by the measurement system and transportable gamma-ray CT. From the experimental data image reconstructions were performed by ML-EM algorithm. The result showed that the CsI detector system can be a suitable component for transportable gamma-ray CT system.